1. Field of the Invention
The present invention relates to a gear pump which provides a pumping effect by rotation of a pair of gears meshing with each other.
2. Description of Related Arts
Gear pumps which are compact and lightweight with simple constructions are conventionally employed in various industrial fields.
In general, such a gear pump has a gear chamber defined between a pair of side plates fitted in a cavity within a housing. A pair of gears meshing with each other are accommodated in the gear chamber. Support shafts of the gears are respectively supported with opposite ends thereof being fitted in support holes formed in the respective side plates. An operating fluid inlet chamber and an operating fluid outlet chamber are respectively provided on opposite sides of a meshing position of the gears in the gear chamber.
In the gear pump, a so-called trapping phenomenon occurs in the vicinity of the gear meshing position, that is, an operating oil is trapped in a region defined between the respective side plates and the gears meshing with each other. When the operating oil trapped in the aforesaid region is compressed by the rotation of the gears, an extraordinarily high pressure is developed in that region, resulting in vibrations and noises.
One approach to this problem is to form relief channels in the side plates adjacent the gear meshing position for releasing the oil trapped in the trap region. The relief channels are provided in pair and include a high pressure side relief channel extending from the vicinity of the gear meshing position to the outlet chamber and a low pressure side relief channel extending from the vicinity of the gear meshing position to the inlet chamber. The pair of relief channels communicate with the trap region in the vicinity of the gear meshing position. The high pressure side relief channel releases the oil trapped in the trap region into the outlet chamber, while the low pressure side relief channel releases the oil trapped in the trap region into the inlet chamber. For prevention of the trapping phenomenon, either of the relief channels should communicate with the trap region at all times.
In order to ensure the pumping effect of the gear pump, on the other hand, communication between the inlet chamber and the outlet chamber should be prevented. Therefore, the pair of relief channels should be prevented from directly communicating with each other and from simultaneously communicating with the trap region. In this respect, the trap region is first brought into communication with the high pressure side relief channel, and then brought into communication with the low pressure side relief channel with the communication with the high pressure side relief channel being blocked, when the meshing of the gears is progressed by the rotation of the gears.
Immediately before the communication with the low pressure side relief channel, the trap region communicates with the high pressure side relief channel and, therefore, has a high inside pressure which is equal to the inside pressure of the outlet chamber. When the trap region communicating with the high pressure side relief channel under the high pressure is instantaneously brought into communication with the low pressure side relief channel, the high pressure trap region communicates with the inlet chamber under a low pressure through the low pressure side relief channel. As a result, the high pressure oil is released into the low pressure inlet chamber, so that impactive noises and vibrations are generated.